1. Field Of The Invention
This invention relates to waste heat steam generators in petroleum refinery catalytic cracker regenerators, and more particularly, to a steam generator having bent, vertically oriented heat exchange tubes therein.
2. Description Of The Prior Art
Existing catalytic cracker waste heat boilers use horizontal "bed coils" to gather heat from the regenerator. Corrosion in and cracking of such horizontal tubes is a problem. These adverse conditions are frequently caused by segregation of the steam-water mix in the tubes and/or the alternate wetting and drying of the top interior surfaces of the tubes, causing abnormal thermal stresses. The present invention which utilizes a bent tube waste heat steam generator with a plurality of substantially vertically oriented tubes eliminates such problems because vertically oriented tubes generally have a longer tube life than horizontal tubes, because of being less subject to the undesirable segregation of the steam and water.
U.S. Pat. No. 1,684,083 to Bloom discloses a refrigerating coil having tubes shaped somewhat similarly to tubes in the heat exchanger in the present invention. The coil is constructed so that practically only dry gas is withdrawn therefrom by the pump in the refrigerating system. In the Bloom device, the refrigerant, as opposed to water in the present invention, passes through an expansion valve as it enters the tubes. Thus, the refrigerant is substantially a vapor when it absorbs heat. This is unlike the present invention in which water is generated into steam by the heat transfer. Further, in the present invention, fluid exiting the heat exchange tubes is normally over 80% liquid by weight. As already indicated, in the refrigeration system of Bloom, practically only dry vapor exits the tubes.
U.S. Pat. No. 3,230,158 to Molique discloses a fired heater with heating tubes shaped somewhat similarly to that of the present invention. The tubes interconnect bottom and top headers. In the present invention, of course, a fired heater is not utilized. Rather, the secondary heat exchange medium is catalyst in a regenerator.
U.S. Pat. No. 4,154,197 to Costello et al. discloses a tube generator with tubes somewhat shaped like the present invention. As with Molique, combustion of fuel is used for heat. The Costello et al. apparatus does not have upper and lower manifolds, but instead, the tubes connect directly to upper and lower water drums. Adjacent tubes in Costello et al. may be joined together by fins to provide vertically and horizontally divided areas in the enclosure. Tubes used in the present invention may be either finned or bare depending on heat exchange requirements and/or fabrication costs. When used, the fins in the present invention extend longitudinally and are spaced radially around the tubes.